JPH0471642A - Planer catalyst for removing nitrogen oxide and its production - Google Patents

Abstract

PURPOSE:To obtain a planer catalyst of high strength by using a catalyst paste containing titanium oxide to which preliminarily silica sol is added, or applying a similar catalyst paste as above mentioned on a screen impregnated with a reinforcing agent comprising a specified material. CONSTITUTION:For a planer catalyst for removing nitrogen oxide which consists of an inorg. fiber woven fabric (screen) coated with a catalyst compsn., a catalyst paste is prepared as the catalyst compsn. by adding silica sol to a catalyst powder essentially comprising titanium oxide. Or, an inorg. fiber woven fabric may be impregnated with a reinforcing agent comprising titanium oxide, silica and polyvinylalcohol, and then dried to obtain a reinforced screen, and then the catalyst paste prepared by adding silica sol to a catalyst powder essentially comprising titanium oxide is applied on this reinforced screen. By heating and molding after coating, the interface area between the screen and the catalyst is further made strong, and thereby, the strength of the catalyst body is significantly increased. Thus, strength and wear resistance of the planer catalyst can be easily increased.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a plate-shaped catalyst for removing nitrogen oxides and a method for producing the same, and particularly to a plate for removing nitrogen oxides in which an inorganic fiber woven fabric is coated with a catalyst composition. The present invention relates to a plate-shaped catalyst for removing nitrogen oxides, which prevents damage to stress-generating portions and improves wear resistance without impairing catalytic activity, and a method for producing the same.

[Conventional technology]

Catalysts that remove nitrogen oxides from exhaust gas (hereinafter simply referred to as catalysts) generally include titanium oxide (Ti0z), molybdenum (MO), tungsten (W), and vanadium (V).
Catalyst compositions made of oxides such as catalytic converters and the like are used in the form of particles, plates, honeycombs, etc. In particular, in the case of boiler exhaust gas that uses fuel such as heavy oil or coal, it is necessary to treat the gas containing large amounts of soot and ash with low pressure loss.
A combination of plate-shaped catalysts, a honeycomb-shaped catalyst with a large aperture ratio, and other catalysts with passages parallel to the gas flow direction are used. Such catalysts include those in which a catalyst component is coated on a metal substrate (Japanese Patent Publication No. 61-28377), catalyst components extruded into a honeycomb shape (Japanese Patent Publication No. 60-3856, etc.), ceramic fiber mats, etc. Many products are known, such as paper formed into a honeycomb shape and coated with a catalyst precursor material (Japanese Patent Publication No. 5B-11253, etc.), and are already in practical use.

[Problems to be Solved by the Invention] Among the above-mentioned conventional techniques, the one in which a catalyst is coated on a metal substrate is superior in that it has a large number of flat plate parts and has low pressure loss and is difficult to accumulate ash. It is large and has the disadvantage that the metal substrate is oxidized.

In addition, when the catalyst component is formed into a honeycomb shape by extrusion, due to the limitations of the forming technology, the formed body is
In order to fill a large-capacity device, which is limited to a size of about 50 mm square and requires several hundred cells, it was necessary to assemble a large number of these small-sized devices. Furthermore, there was a problem that the molded body was weak against impact force.

Furthermore, inorganic fiber cloth or paper whose surface is coated with a catalyst component has a problem that, although it is strong against impact forces, it has low mechanical strength and is abraded by ash particles contained in exhaust gas.

Therefore, in order to solve these problems, there is an unpublished application that is an invention of the inventors. That is, an inorganic fiber woven fabric (hereinafter referred to as a ceramic screen or simply a screen) is impregnated with inorganic oxide fine particles to strengthen it, and a catalyst composition containing titanium oxide as a main component and cotton-like inorganic fibers are added to it with water. The material is coated with a paste or slurry that has been dispersed and mixed into the material, and then compacted using a roller press or the like.

However, compressive stress is generated at the ends and corrugated portions of the plate-shaped catalyst based on the ceramic screen or the like due to the pressure of the fluid or its own weight, which may lead to damage or even destruction. In addition, the thin plate may cause damage during handling, and especially in denitrification equipment for boilers that use coal as the main fuel, a large amount of soot and dust contained in the exhaust gas may damage the surface of the catalyst and the end face of the catalyst corresponding to the gas inlet. It is also conceivable that the material may be easily worn out, affecting its activity, or even being damaged. A common way to improve the strength of such catalysts is to add inorganic oxide fine particles such as silica sol to the catalyst molded body or raw materials. A method of forming a gel to achieve high density reinforcement (for example, Japanese Patent Application Laid-Open No. 55-15574)
0), or a method for producing a catalyst by directly mixing titanium sulfate, titania powder, or finely divided silicic acid to improve moldability, heat resistance, and increase bonding strength due to the surface effect of fine silica particles (e.g., Japanese Patent Publication No. 56) -633
4 and Japanese Patent Publication No. 1-14807). In the former method, as the impregnation process progresses, only the silica content is impregnated into the catalyst, and the solid concentration on the impregnating liquid side becomes thinner. Therefore, in order to stabilize the product characteristics, the solid concentration in the impregnating liquid must be strictly controlled. proper management is required. Furthermore, it is influenced by the characteristics of the catalyst material that is the material to be impregnated, such as pore distribution, and if certain characteristics are to be obtained after impregnation, it is necessary to minimize variations in the properties of the material to be impregnated. From an industrial perspective, it is undesirable to increase the number of impregnation steps in the manufacturing process. On the other hand, in the latter method, silica sol is mixed in advance with the catalyst raw material, mainly for the purpose of increasing the bonding force between particles, but as in the powder method, the screen and catalyst components are composited to achieve high strength. In a molded article, strength cannot be improved simply by improving particle bonding.

As described above, there is no example of using a paste containing a catalyst component mixed with silica sol to improve the strength of a plate-shaped catalyst molded body using a screen like the powder method.

The present invention eliminates such problems of the prior art, reduces variations in product properties through a simple manufacturing process, and generates compressive stress without impairing activity in a plate-shaped catalyst based on inorganic fiber woven fabric etc. The present invention relates to a plate-shaped catalyst for removing nitrogen oxides, which is suitable for preventing crushing of parts and damage during handling, and also for preventing abrasion and damage of a catalyst layer due to soot and dust in exhaust gas, and a method for producing the same.

[Means to solve the problem]

The problem with the prior art described above is that in plate-shaped catalysts for nitrogen oxide removal in which inorganic fiber woven cloth is coated with a catalyst composition, silica sol is added in advance to catalyst powder containing titanium oxide as the catalyst composition. A plate-shaped catalyst for removing nitrogen oxides characterized by using a paste, and a method for producing a plate-shaped catalyst for removing nitrogen oxides, in which a catalyst component is applied to an inorganic fiber woven fabric, and then dried and fired,
An inorganic fiber woven fabric is impregnated with a reinforcing agent consisting of titanium oxide, silica, and polyvinyl alcohol, and then dried to form a reinforcing screen, and a catalyst paste made by adding silica sol to a catalyst powder containing titanium oxide as a main component is used for the reinforcement described above. The problem is solved by a method for producing a plate-shaped catalyst for removing nitrogen oxides, which is characterized by coating the catalyst on a screen, drying it, and baking it.

[Effect]

Ceramic screen (inorganic fiber woven fabric) like this catalyst
It is known that the interface between the screen and the catalyst affects the strength characteristics of the structure using the screen, and when applying the catalyst paste, the way the paste wraps around the screen is important. By mixing silica sol in the paste, which flows like water, the fluidity of the paste can be made better than a water-only catalytic paste for the same particle concentration, thus reducing the impact on the screen when applied. It wraps around well, has a strong interface with good adhesion, and has little damage to the screen. Furthermore, from the viewpoint of wear resistance, it is necessary to reduce the water content in the paste and improve the catalyst density, but with the silica sol mixture of the present invention, even if the water content is reduced, the fluidity of the paste remains Good and leads to improved wear resistance.

In addition, by heating and forming the silica sol at a predetermined temperature while applying a load with a roller or press after application, the silica sol, which behaved like water in the paste, evaporates and becomes a porous silica gel. In addition to bonding the catalyst particles near the surface, the interface between the screen and the catalyst is further strengthened, so the strength characteristics of the catalyst body are significantly improved. Therefore, the catalyst body after heat molding can be easily handled, and damage at that time can be reduced. .

Furthermore, by finally firing the catalyst body, the bonding force of the catalyst particles is developed and the strength is further increased, and combined with the above action, a high-density catalyst body with a strong interface with the screen is obtained. It can withstand peeling of the interface due to coal ash and abrasion of catalyst particles, and can achieve the above goals. Moreover, since the silica sol filled inside the catalyst is finely porous, even if the density is increased in this way, the denitrification rate will not decrease much.

〔Example〕

The catalyst preparation process for the entire configuration is shown in Figure 1.
A reinforced screen was prepared by impregnating a reinforcing agent consisting of three components, TiOz/SiO and /PVA (polyvinyl alcohol), to improve heat resistance and prevent damage during molding, and then drying. Furthermore, in this catalyst, for the purpose of activation and protection, catalyst powder/
Pre-coated with 5i08 slurry. Next, a catalyst paste mixed with silica sol, which will be described in detail below, is sandwiched between the two screens, supplied between a pair of upper and lower rollers, and rolled and coated at a speed of 7.5 m/min. The catalyst was then fed between heating rollers with a corrugated shape, heated and formed at a temperature of 200'C, and finally fired at 550'C/2 h to obtain a catalyst body.

Preparation of Catalyst Paste (a) Preparation of Catalyst Composition Fine Particles (Catalyst Powder) 77 moj7 of metavanadate (
NH4voi) 0.85 kg, and ammonium molybdate ((NH4).

Add 2.16 kg of Mot Oz4・4Hz O),
The mixture was kneaded using a kneader heated to 140° C. while evaporating water. The resulting paste-like material with a moisture content of 38% was formed into a columnar shape of 3 mφ using an extrusion granulator, and then dried using a fluidized bed dryer. After baking the dried granules at 550°C for 2 hours while blowing air, 20 tons of
The particles were pulverized to a particle size of 90% or more of 1 m or less to obtain catalyst composition fine particles.

(b) Preparation of catalyst paste The above catalyst composition fine particles have a particle diameter of 12 nm and a particle concentration of 20 nm.
After adding and mixing a predetermined amount of acidic silica sol (wt%), Kaowool short fibers were added together with a small amount of water so that the amount was 15wt% based on the catalyst composition fine particles, and kneaded for 1 hour in a kneader to prepare the present example catalyst. 1 was prepared. Similarly, Example Catalyst 2 was prepared using acidic silica sol having a particle diameter of 12 nm and a particle concentration of 33 wt%. The SiO□/catalyst powder component ratio and water content of these prepared pastes are shown in FIG. Further, as a comparative example catalyst, a catalyst was prepared under the same conditions without adding silica sol.

The present example catalyst and the comparative example catalyst were tested for bending strength, peeling resistance, and NOx removal rate according to the bending strength test method shown in Figure 7, the hardness test method shown in Figure 8, and the NOx removal rate measurement conditions shown in Table 1. was measured.

First, FIG. 2 shows the relationship between the water content in the catalyst paste and the penetration degree. Penetration is an index that indicates the consistency of asphalt, etc., and the measurement principle is to measure the penetration depth when a needle carrying a certain weight is pressed against the material to be measured for a certain period of time.

The test of the present invention was conducted according to the method specified in JIS K 2208. This example catalyst paste 1.
In both cases, the penetration degree was greater than that of the comparative catalyst paste.
That is, it shows that the fluidity is good. Also,
At the same penetration level, the paste of this example had a lower moisture content than the comparative example, which indicates that it is possible to increase the density of the catalyst body after coating. The penetration must be at least 60; if it is less than that, the paste will be too hard and there is a risk of damaging the screen during application.For this reason, the addition of silica sol improves fluidity and strengthens the paste. This can be said to be an effective method for achieving this goal. In addition, it is best to add silica sol directly to the dried catalyst powder fine particles; if it is added after mixing the catalyst powder and water, the silica sol will not penetrate uniformly into the catalyst powder, and the addition effect will not be fully expressed. .

Next, the strength characteristics of the catalyst molded body are shown in FIG.

This figure shows the load-displacement curve of the bending test specimen, and the initial slope (
Young's modulus), the catalyst of the present example is clearly larger than the catalyst of the comparative example. This result shows that the filling of silica sol results in a paste with good fluidity.
This is thought to be due to the fact that by heating and forming the silica sol while applying a load to the area where the wraparound to the screen was improved, the silica sol turned into a gel, resulting in even better adhesion, reinforcing the interface and increasing the density. By increasing the strength in this way, the handling properties of the plate-shaped catalyst bodies during production are improved, and even in actual plants containing coal ash, it is possible to prevent abrasion of the catalyst particles and peeling of the interface part M. is considered possible.

Further, FIGS. 4 and 5 show the relationship between the 5iOt/catalyst ratio, the amount of water in the catalyst paste, and the scratch width of the catalyst body, respectively. The scratch width (see FIG. 8) tends to become smaller as the SiO□/catalyst ratio increases and as the amount of water in the catalyst paste decreases. It is thought that a small scratch width means that particles are difficult to peel off, that is, it is related to wear resistance. Currently, impregnated catalysts with a service life of 5 years or more, which have been used in actual coal-fired plants, have a scratch width of 0.
It is around 20 gardens, and from this it is at least 0.22m.
It is thought that a strength of n+ or less is required. From the viewpoint of wear resistance, it can be said from FIG. 4.5 that it is desirable to add silica sol so that the SiO□/catalyst ratio is 0.08 or more and the water content in the catalyst paste is 25 wt% or less. Although the effects of the present invention are achieved regardless of the particle size of the silica sol, it is desirable to use particles with an average diameter of 25 nm or less in terms of wear resistance.

Next, the influence on the denitrification rate was investigated, as shown in Figure 6.The value of the comparative example catalyst was 1.
If this is the case, the catalyst of this example has a small reduction rate of 0.95 to 0.85, and it can be said that there is no particular problem.

The characteristics and physical properties of the catalyst of the present invention are summarized in the blank table below. According to the present invention, unlike the impregnation method, it is not affected by the properties of the impregnating strengthening liquid and the properties of the catalyst to be impregnated. It is possible to produce catalysts with stable properties. Furthermore, since there is no need to add a new strengthening step to the manufacturing process, a high-strength catalyst can be obtained with a simple preparation method.

In the present invention, the catalyst paste was mixed with silica sol and applied to the screen to obtain the catalyst body, but other materials such as T
It is also possible to prepare a paste by mixing it with fine particles such as iOz and apply it to a screen as a catalyst carrier.

〔Effect of the invention〕

According to the present invention, it is possible to easily increase the strength and wear resistance of the plate-shaped catalyst with a simplified manufacturing process, so that it is possible to prevent crushing of compressive stress generating parts, prevent damage during handling, and further prevent foreign particles from collapsing. , which is highly effective in preventing damage caused by dust collisions.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the preparation process of the catalyst of the present invention, FIG.
The figure shows the relationship between water content, component ratio, and penetration in the paste of the example catalyst of the present invention and the comparative example catalyst. Figure 3 is a load-displacement curve diagram of the present invention and the comparative example catalyst. , Figures 4 and 5 are diagrams showing the results of the hardness test of the prepared catalyst body, Figure 6 is a diagram showing the denitrification rate of the catalyst of the present invention, and Figures 7 and 8 are diagrams showing the evaluation of the characteristics of the catalyst. It is a figure showing the bending test method and the hardness test method used for this purpose. Applicant Babcock-Hitachi Co., Ltd. Agent Patent Attorney Takeshi Kawakita 2 Figure: Relationship between water content and component ratio in rejuvenating paste and sensitization moisture content bk (w+'/,) ): 5i (J2 catalyst powder wood ratio) Displacement (mrn) Fig. Relationship between SiO□/catalyst component ratio and bow width Fig. Relationship between moisture in catalyst paste 11 and scratching radius Moisture paper (wt'10)

Claims (6)

[Claims] (1) In a plate-shaped catalyst for nitrogen oxide removal in which an inorganic fiber woven fabric is coated with a catalyst composition, a catalyst paste prepared by adding silica sol to a catalyst powder containing titanium oxide as a main component is used as the catalyst composition. Characteristic plate-shaped catalyst for removing nitrogen oxides. (2) In claim (1), the weight ratio of silica (SiO_2) to catalyst particles in the catalyst paste is from 0.08 to
A plate-shaped catalyst for removing nitrogen oxides, characterized in that the nitrogen oxide removal ratio is 0.2. (3) In a method for producing a plate-shaped catalyst for removing nitrogen oxides, which comprises applying a catalyst component to an inorganic fiber woven fabric, then drying and baking it,
An inorganic fiber woven fabric is impregnated with a reinforcing agent consisting of titanium oxide, silica, and polyvinyl alcohol, and then dried to form a reinforcing screen, and a catalyst paste made by adding silica sol to a catalyst powder containing titanium oxide as a main component is used for the reinforcement described above. A method for producing a plate-shaped catalyst for removing nitrogen oxides, which comprises coating the catalyst on a screen, drying it, and firing it. (4) The method for producing a plate-shaped catalyst for removing nitrogen oxides according to claim (3), characterized in that the catalyst paste is prepared to have a penetration of 60 or more. (5) The method for manufacturing a plate-shaped catalyst for removing nitrogen oxides according to claim (3), characterized in that the reinforcing screen is precoated with a mixed slurry of catalyst powder and silica, and then the catalyst paste is applied. (6) The plate-shaped catalyst for removing nitrogen oxides according to claim (3), characterized in that after applying a catalyst paste to the reinforcing screen, it is molded into a predetermined shape while heating, and this molded body is dried and fired. manufacturing method.